There are thought to be about 300 of the whales, which have been listed as an endangered species since 1973.

Amos said he was skeptical when he first heard the report, because the whales are so rare. He photographed the whales to report them to federal officials that monitor them.

"It's a real thrill, a once-in-a-lifetime opportunity to see such a rare animal," he said. "But also we felt some concern because they shouldn't be where they are."

Amos said the calf appeared to be suckling, and it had two cuts on its back. The mother looked about 45 feet long, while the calf was about 20 feet, he said.

A spokesman said the U.S. Coast Guard had also responded to monitor the whale's condition. The Coast Guard was asking captains on the Corpus Christi Bay and surrounding areas to try to avoid the whales.